Process for preparing alkali metal-lead soap base greases



United States Patent PROCESS FQR PREPARING ALKALI MET AL-LEAD SOAP BASE GREASES Terence B. Jordan, Fishkill, N. Y., assignor to The Texas Company, New York, N. Y., a corporation of Delaware N0 Drawing. Application May 2, 1956 Serial No. 582,068

9 Claims. (Cl. 252-36) This invention relates to a process for preparing mixed alkali metal-lead soap base greases. More particularly, this invention discloses a process whereby mixed alkali metal-lead soap base greases, useful as extreme pressure greases, are obtained in high yield.

Prior to this invention, it has not been possible to obtain good yields of mixed base grease containing a lead soap because of the difficulty in obtaining complete reaction of lead oxide with the soap precursor. It has also been difficult to control the free lead oxide or free acid content of the grease. The process of this invention assures complete reaction of the lead oxide with the soap precursor, permits close control of the free lead oxide or free acid content of the grease and results in improved yields of the mixed alkali metal-lead soap base grease.

In accordance with the process of this invention, mixed alkali metal-lead soap base grease is prepared by a procedure involving the following steps. The lead soap is first formed by reaction of lead oxide with an excess of soap precursor in a mineral oil lubricating base in the presence of water at a temperature above 300 F. The reaction mixture is then cooled to a temperature below 230 F. and the alkali metal soap is formed by reacting alkali metal hydroxide with unsaponified soap precursor at a temperature below about 230 F. in the presence of water. After alkali metal oxide saponification is complete, the reaction mixture is heated to a temperature above 300 F. for dehydration, oleaginous lubricating base is added, and the grease mixture is then cooled. Additives such as antioxidants and extreme pressure agents are added at a temperature below about 230 F. during the second stirred cooling of the grease. Mixed alkali metal-lead soap base greases are obtained by the process of this invention in substantially better yields than by previous methods of preparing these greases.

The alkali metals most commonly employed in the formulation of grease compositions are sodium, lithium and potassium. The other alkali metals, cesium and rubidium, are normally not employed because of cost and/or availability. In further description of. the invention, the invention will be illustrated by sodium and lithium soaps.

The soap concentration of the greases produced by this invention is to 30 weight percent of the grease with concentrations between 8 and 20 weight percent normally being employed. The weight ratio of alkali metal soap to lead soap is between 1:1 and 9:1. Generally, the alkali metal soap is used in an amount between 1.5 and 6 times the amount of lead soap.

The process of the invention is eflfective with a great variety of soap precursors. Fatty acids, their glycerides and monoesters, hydroxy fatty acids, their glycerides and esters are usable in the process of the invention if the acid contains 10 to 24 carbon atoms. The fatty acidtype soap precursor is illustrated by the following: stearic acid, oleic acid, palmitic acid, myristic acid, lauric acid, taliow, cottonseed oil, menhaden oil, lard oil and soybean oil. The hydroxy fatty acid-type soap precursor is illustrated by the following: 12-hydroxy stearic acid, 9-hydroxy stearic acid, IO-hydroxy stearic acid, 8-hydroxy myristic acid, 6-hydroxy lauric acid, 9,10-dihydroxy stearic acid, castor oil, methyI-IZ-hydroxy stearic acid, ethyl-12-hydroxy stearic acid and hydrogenated castor oil.

The process of the invention is only effective when a mineral lubricating oil is employed as the oleaginous base for the formation of both the lead soap and the alkali metal soap. Attempts to obtain improved yields of mixed alkali metal-lead soap base greases employing an ester type synthetic lubricating oil as a base oil for the formation of the lead and alkali metal soaps have been unsuccessful. Accordingly, the process of the invention utilizes a mineral lubricating oil as the base oil in the formation of the lead and alkali metal soaps. Where an ester type synthetic lubricating oil is employed as a component of the total oleaginous lubricating base, such synthetic oil is added following dehydration and preferably after cooling below about 280 F. The mineral lubricating oil constitutes at least 15 weight percent of the total oleaginous lubricating base.

The mineral lubricating oil used for the formation of the lead and alkali metal soaps may be selected from oils having an SUS at 100 F. of about 50 up to an SUS at 210 F. of about 150. Distillate and residual fractions of parafiin, naphthene and mixed paraflin-naphthene base crudes are usable as the base oil in the formation of the lead and alkali metal soaps. A preferred mineral lubricating oil for low temperature grease properties is a distillate fraction having an SUS viscosity at 100 F. between 50 and 350. A preferred mineral lubricating oil for superior high temperature and non-bleeding grease properties is a residual-distillate blend having an SUS at 210 F. between 70 and 100 or higher.

The synthetic oleaginous lubricating oils which can be used in finishing a grease to the desired grade are usually either polyesters, polyethers or their thio analogs. The most commonly used synthetic lubricating oils are diesters of aliphatic dicarboxylic acids containing at least 6 carbon atoms. Di-Z-ethylhexyl adipate, di-amyl-sebacate and thiooctyl azelate are examples of the most commonly used synthetic lubricating oils.

Additives to impart antioxidant and extreme pressure properties may be incorporated in the mixed alkali metallead soap base greases of this invention during the cooling step subsequent to the dehydration. Aromatic amine type inhibitors have been found particularly effective antioxidants for alkali metal-lead soap base greases; aromatic amines such as tetramethyl diamino diphenyl methane, diphenyl amine and phenyl alphanaphthyl amine are preferred. Extreme pressure additives which may be incorporated in the greases are sulfurized fats, sulfurized oils, chlorinated organic compounds such as chlorosubstituted waxes, chlorosubstituted aromatic compounds and chlorinated olefin polymers and sulfo-chlorinated compounds such as sulfo-chlorinated olefin polymers and olefins derived from waxes.

Mixed base greases which are obtained in improved yield by the process of the invention are illustrated by the following grease compositions: 10% lithium stearate, 5% lead stearate, mineral lubricating oil; 10% p0- tassium stearate, 5% lead stearate, 85% lubricating oil; 10% sodium stearate, 3% lead stearate, 82% lubricating oil; 10% lithium hydroxy stearate, 2.5% lead stearate, 82.5% lubricating oil; 12% lithium l2-hydroxy stearate, 3% lead l2-hydroxy stearate, 82% lubricating oil.

The reaction of lead oxide with an excess of soap precursor in a mineral lubricating oil in the presence of water is effected at temperatures between 300 and 360 F. with temperatures of 305 to 330 F. being preferred.

3 Since water is rapidly removed from the reaction zone at atmospheric temperature under these conditions, it is advisable to effect the reaction under pressure or with incremental addition of water during the reaction of the lead oxide and the soap precursor.

After complete reaction of lead oxide with the fatty material, the reaction mixture is cooled to a temperature below 230 F. and usually between 190 and 230 F. The cooling can be accomplished by the addition of a small amount of some oil or additional fatty material in conjunction with indirect heat exchange. The free soap precursor in the reaction mixture is then sapom'fied with an alkali metal hydroxide in the presence of a small amount of added water. The addedwater is the conventional amount used in the formation of alkali metal soap greases. Subsequent to saponification, the reaction mixture is dehydrated at a temperature above 300 F., for example between 310 and 360 F.

In mixed lead-lithium base greases it has been found that the dehydrated mixture is advantageously heated to a temperature between 400 and 450 F. to melt the soap components prior to the addition of the remainder of the oil. The elevation of the reaction mixture to the temperature between" 400 F. and 450 F. is a preferred modification of the process of the invention since much better yields are thereby obtained.

The remainder of the oil is added subsequent to the dehydration at a temperature between 300 and 360 F. or subsequent to heating the mass to 400 F. The remainder of the grease formation is conventional.

The following examples illustrate the effectiveness of the process of the invention in obtaining improved yields of mixed alkali metal-lead soap base greases.

Example I illustrates the prior art method of producing alkali metal-lead soap base greases. Examples II to IV are the improved results obtained by the process of the invention.

Example I To a grease kettle there were charged 18.4 pounds of 12-hydroxy stearic acid, 12.0 pounds of an acid-treated paratfin base distillate oil having an SUS at 100 F. of 100, 12.0 pounds of water and 1.39 pounds of litharge. The reaction mixture was saponified at a temperature of 180 to 200 F. for one hour after which 12.8 pounds of a 9.6% aqueous solution of lithium hydroxide was added in increments and Saponification continued for an additional 4 hours. After Saponification, the reaction mixture was dehydrated at 250 to 300 F. for 11.5 hours. An additional 2.0 pounds of the same oil used above was added during this period to facilitate mixing of the soap base. After dehydration, 42.0 pounds of di-Z-ethylhexyl adipate (Plexol 244) was added as the grease mixture was slowly cooled with stirring. The resulting grease mixture had the following calculated composition:

Percent by wt.

Despite the fact that the total soap concentration was 26.3%, the resulting grease was a No. NLGI grade, as indicated by the following tabulation of ASTM penetrations:

Unworked 200 Worked 362 Dropping point, F 362 Example II To a grease kettle there were charged 14.8 pounds of 12-hydroxy stearic acid, 2.2 pounds of water, 7.0 pounds of the same mineral oil employed in Example I and 1.14 pounds of litharge.

The reaction mixture was saponified 4 at a temperature of 300 to 330 F. for 3 hours and then cooled with stirring to 200 to 210 F at which point 10.9 pounds of a 10.2% aqueous solution of lithium hydroxide was added. Saponification of lithium hydroxide and acid was efiected at a temperature between 190 and 210 F. for 1 hour. The reaction mixture was then dehydrated at a temperature of 300 to 330 F. for 4 hours. Six pounds of the same mineral oil employed in Example I was added followed by 39.0 pounds of di-Z-ethylhexyl adipate, as the reaction product was slowly cooled with stirring. The resulting grease had the following calculated composition:

Percent by wt. Lithium 12-hydroxy stearate 17.6

The product, having a total soap concentration of 23.5%, was a No. 2 grade grease, as evidenced by the following tabulation of ASTM penetrations:

Unworked 203 Worked 263 Dropping point, F 408 Example III To a grease kettle were charged 14.8 pounds of 12- hydroxy stearic acid, 7.0 pounds of the same base oil used in Example I, 2.2 pounds of water and 1.14 pounds of litharge. After the reaction product was aponified for 1 hour at a temperature of 300 to 330 F., the reaction mixture was cooled to a temperature of 200 to 210 F. and the addition of 11.2 pounds of 9.9% aqueous lithium hydroxide in increments was initiated. After Saponification of the lithium hydroxide and acid for 2.5 hours at 180 to 210 F., the reaction mixture was dehydrated at a temperature between 280 and 330 F. for 10 hours, during which time an additional 6.0 pounds of the mineral oil employed in Example I was added to facilitate working of the soap base and to provide the desired dehydration temperature. Following dehydration, an additional 44.7 pounds of the mineral oil employed in Example I was added as the reaction mixture was lowly cooled with stirring. The resulting grease had the following calculated composition:

Percent by wt.

This product, having a total soap concentration of 20.3%, was a No. 1 grade grease as indicated by the following tabulation of ASTM penetrations:

Unworked 191 Worked 300 Dropping point, F 359 Example IV To a grease kettle there were charged 7.1 pounds of the methyl ester of 12-hydroxy stearic acid and 10.0 pounds of a mineral oil consisting of 20% by volume of an acid-treated parafin base distillate oil and by volume of a deasphalted, solvent refined, dewaxed naphthenic residual oil. The residual-distillate mineral oil blend had an API gravity of 25.5", a flash (C. O. C.) of 465 F., and SUS viscosity at F. of 1041 and at 210 F. of 82.5, and a pour point of 0 F. This mixture was heated to 300-330 F. and 0.71 pound of litharge added in increments alternately with increments of water to accelerate formation of lead soap. After reaction of litharge was complete the mixture was cooled to 200-230 F. by stirring and by the addition of 10 pounds of the mineral oil blend used with the original kettle charge.

At ZOO-230 F., 5.0 pounds of a aqueous solution of lithium hydroxide was added in increments. After saponification of the lithium hydroxide and methyl ester of 12-hydroxy stearic acid for 1 hour, the reaction mixture was heated to a temperature of 300 F. and 22.1 pounds of the mineral oil base described above was added. The reaction mixture was heated to a temperature above 400 F. and dehydrated at a temperature between 400 and 450 F. for 1 hour. The mixture was cooled by circulating through a heat exchanger and a disperser. An additional 20.0 pounds of the mineral oil base described previously under this example was added over a temperature range of 340 to 280 F. At 230 F., 0.35 pound of diphenylamine was added. The final mixture was cooled to 200 F. The resulting grease had the following calculated composition.

Percent by wt.

Despite the fact that the above grease had only a total soap concentration of 10.6%, the product was approximately a No. 2 grade as indicated by the following tabulation of ASTM penetrations:

Unworked 252 Worked 264 Dropping point, F. 385

The foregoing examples demonstrate the improved yields of alkali metal-lead soap base greases obtained by the process of the invention. Examples I and II are particularly pertinent. In Example I, wherein the prior art procedure was employed, a No. 0 grade grease was obtained despite the fact that the soap concentration was as high as 26.3 weight percent. In contrast, in Example II, employing the process of the invention, a No. 2 grade grease was obtained despite the fact that the total soap concentration was only 23.5 weight percent. In

xample III a No. 1 grade grease was obtained although the soap content was only 20.3 weight percent. Example IV illustrates the unusually superior yields obtained by employing the high heat modification with a lithium-lead soap base grease.

Obviously, many modifications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof and, therefore, only such limitations should be imposed as are indicated in the appended claims.

I claim:

1. A process for preparing a mixed alkali metal-lead soap base grease which comprises forming a lead soap by reaction 01 lead oxide, PbO, with an excess of soap precursor in a mineral base lubricating oil at a temperature between 300 and 360 F. in the presence of water, cooling the reaction mixture to a temperature between 290 and 330 F., forming an alkali metal soap by reacting alkali metal hydroxide in the presence of water with the unsaponified portion of said soap precursor at a temperature between and 230 F., said lead oxide and alkali metal hydroxide being reacted with said soap precursor in such proportions that there is formed a substantially neutral product in which said alkali metal soap and said lead soap are in a ratio of from 1:1 to 9:1, dehydrating said reaction mixture at a temperature between 300 and 450 F. and adding a lubricating oil to said reaction mixture during cooling to obtain the desired grease grade.

2. A process according to claim 1 in which reaction of lead oxide with soap precursor is carried out at a temperature between 300 and 330 F.

3. A process according to claim 1 in which the oleaginous lubricating base added to the reaction mixture during cooling to the desired grease grade is a mineral lubricating oil.

4. A process according to claim 1 in which the oleaginous lubricating base added to the reaction mixture during cooling to the desired grease grade is an esterbase synthetic lubricant.

5. A process for preparing a mixed lithium-lead soap base grease which comprises forming a lead soap by reaction of lead oxide, PbO, with an excess of soap precursor in a mineral base lubricating oil at a temperature between 300 and 360 F. in the presence of water, cooling the reaction mixture at a temperature between 190 and 230 F., forming said lithium soap by reacting lithium hydroxide in the presence of water with the unsaponified portion of said soap precursor at a temperature between 190 and 230 F., said lead and lithium hydroxide being reacted with the soap precursor in such proportions that there is formed a substantially neutral product in which said alkali metal soap and said lead soap are in a ratio of from 1:1 to 9:1, dehydrating said reaction mixture at a temperature between 300 and 400 F. and adding a lubricating oil to said reaction mixture during cooling to obtain the desired grease grade.

6. A process according to claim 5 in which the dehydration of the lead-lithium soap base grease is effected at a temperature between 400 and 450 F.

7. A process according to claim 5 in which reaction of the lead oxide with soap precursor is effected at a temperature between 300 and 330 F.

8. A process according to claim 5 in which the soap precursor is 12-hydroxy stearic acid.

9. A process according to claim 5 in which the soap precursor is the methyl ester of 12-hydroxy stearic acid.

References Cited in the file of this patent UNITED STATES PATENTS 2,295,189 Swenson Sept. 8, 1942 

1. A PROCESS FOR PREPARING A MIXED ALKALI METAL-LEAD SOAP BASE GREASE WHICH COMPRISES FORMING A LEAD SOAP BY REACTION OL LEAD OXIDE, PBO, WITH AN EXCESS OF SOAP PRECURSOR IN A MINERAL BASE LUBRICATING OIL AT A TEMPERATURE BETWEEN 300 AND 360*F. IN THE PRESENCE OF WATER, COOLING THE REACTION MIXTURE TO A TEMPERATURE BETWEEN 290 AND 330*F., FORMING AN ALKALI METAL SOAP BY REACTING ALKALI METAL HYDROXIDE IN THE PRESENCE OF WATER WITH THE UNSAPONIFIED PORTION OF SAID SOAP PRECURSOR AT A TEMPERATURE BETWEEN 190 AND 230*F., SAID LEAD OXIDE AND ALKALI METAL HYDROXIDE BEING REACTED WITH SAID SOAP PRECURSOR IN SUCH PROPORTIONS THAT THERE IS FORMED A SUBSTANTIALLY NEUTRAL PRODUCT IN WHICH SAID ALKALI METAL SOAP AND SAID LEAD SOAP ARE IN A RATIO OF FROM 1:1 TO 9:1, DEHYDRATING SAID REACTION MIXTURE AT A TEMPERATURE BETWEEN 300 AND 450*F. AND ADDING A LUBRICATING OIL TO SAID REACTION MIXTURE DURING COOLING TO OBTAIN THE DESIRED GREASE GRADE. 